The system disclosed in the present application is a machine fed continuously with jars. The machine uses electro-optic means to detect foreign matter on the surface of the glass or on the glass surface of the jars and to reject the bad jars.
An "electric eye" is not satisfactory to inspect jars for foreign matter for two reasons: (1) the system looks for small dark spots on a proportionally large bright area. There are light sensors but not darkness sensors, so the proportional effect of a small dark spot in a bright field is indeed small and can be considered unmeasurable by any bulk light transmission measurement system; (2) the adverse optical properties of the jar are: (a) a jar is glass and reflects and refracts light; (b) the ridge molded into the bottom acts like a short focal length lens; (c) raised letters and numerals, logo, and other indicia act as light focusing and scattering means; (d) there are no plane surfaces in the basic jar structure; (e) four distinct regions must be examined: side, top shoulder, bottom shoulder, and bottom; (f) two seams created at mould parting lines extend down the sides and have optical properties that vary from jar to jar; and (g) the kick out plunger of the mold has scored a circular mark on the bottom of the jar.